Social problems have recently arisen from the brittleness and durability of cement structures, for example, destruction of bridges caused by earthquakes, rust formation on reinforcing bars caused by the neutralization of concrete, the fatigue of reinforcing steels caused by a sharp increase in traffic volumes, and the like. Replacing the structures with new ones is naturally satisfactory. However, replacing them is very costly.
When a pier of an elevated structure is taken as an example, a method for reinforcing the pier by bonding a steel sheet to the column containing concrete with an adhesive and a method for reinforcing it by bonding sheet-like reinforcing layers containing carbon fibers have been employed as countermeasures. In particular, the latter method has come to be adopted recently because the reinforced structures show significant reinforced effects and excellent durability, and because the reinforcing operation is simple. In the sheet-like reinforcing layers containing carbon fibers mentioned above, a number of carbon fibers are arranged in parallel in one or two directions. For example, Japanese Patent Kokai Publication Nos. 5-332031 and 7-243149 propose fibrous sheets for structure reinforcement in which carbon fibers are arranged in one direction. According to the former patent publication, carbon fiber bundles each containing a number of collected carbon fibers are arranged on an auxiliary sheet in one direction through an adhesive layer. According to the latter patent publication, carbon fibers are unidirectionally pulled mutually in parallel and in a sheet-like manner to form a sheet surface, and a weave structure is formed with transverse direction secondary fiber bundles and longitudinal direction secondary fiber bundles parallel to the carbon fibers, both types of the bundles being situated on respective sides of the sheet, to hold the sheet-like carbon fiber bundle arranged in one direction.
Furthermore, Japanese Patent Kokoku Publication Nos. 57-52221 and 8-23096 propose fibrous sheets for structure reinforcement in which carbon fibers are bidirectionally arranged.
According to the former patent publication, two carbon fiber bundles the carbon fibers of which are pulled unidirectionally and mutually in parallel in a sheet-like manner within each bundle and which face each other form a bidirectional sheet surface. The sheet surface is made to form a weave structure by longitudinal secondary fibers and transverse secondary fibers which are parallel to the respective fiber bundles, and is integrally held. According to the latter patent publication, a bias fabric is formed by a longitudinal carbon fiber bundle and a transverse carbon fiber bundle extending obliquely in relation to the longitudinal carbon fiber bundle, and the carbon fibers are bidirectionally arranged on the bias.
These unidirectional or bidirectional fibrous sheets for structure reinforcement are prepared to display the excellent high strength and high elastic modulus of the carbon fibers in the fiber axial direction as much as possible. Moreover, an auxiliary sheet and secondary fibers other than the carbon fibers are used to integrally hold the carbon fibers and obtain a fibrous sheet for structure reinforcement having a decreased fiber slippage within a sheet. That is, though a woven fabric is generally prepared by mutually intersecting warps and wefts to have a decreased fiber slippage, the constituent fibers are markedly bent at the intersectioning points of the warps and wefts. As a result, when a stress is applied to the fabric, the stress is concentrated at the bent portions, and in a woven fabric consisting of carbon fibers, the inherent high strength and high elastic modulus of carbon fibers cannot be displayed.
However, in spite of the improvement of the fibrous sheet for structure reinforcement as described above, a coarse fibrous sheet for structure reinforcement having a decreased fiber slippage, a high toughness unidirectionally or bidirectionally and numerous spaces among reinforcing fibers in a sheet is not obtained currently. To reinforce, for example, a column containing concrete by the use of the fibrous sheets for structure reinforcement, the concrete to be reinforced is first coated with an adhesive and the concrete is subsequently wound with the fibrous sheet while the sheet is being pressed, followed by coating the fibrous sheet with an adhesive to form a reinforcing layer. In order to make the fibrous sheet for structure reinforcement function as a reinforcement layer, it is important that the adhesive should penetrate sufficiently among fibers within each of the fiber bundles and among the fiber bundles. To meet the requirement, the fibrous sheet for structure reinforcement must have spaces the adhesive can penetrate among the reinforcing fibers forming the fibrous sheet, namely among fibers within each of the fiber bundles and among the fiber bundles. In general, when the spaces among the fibers in the fibrous sheet for structure reinforcement become large, there arise problems that the slippages among fibers become large and that the toughness falls in the arrangement direction of the fibers. Accordingly, the fibrous sheet for structure reinforcement can fulfill its role as a reinforcing layer of a member to be reinforced only after the fibrous sheet sufficiently meets the three requirements mentioned above.
Disclosure of Invention
An object of the present invention is to solve the problems associated with the prior art as mentioned above, and provide a fibrous sheet for structure reinforcement which has a decreased slippage within the sheet, a high toughness in the arranged directions of the fibers (one or two directions), numerous spaces among fibers and good penetration of an adhesive, as a fibrous sheet for reinforcing not only general structures but also piers of elevated structures, columns and walls of buildings, and the like, which also facilitates handling during execution of works and which has lightness of the reinforcing layer, and a structure reinforced with the sheet.
The present inventors have intensively conducted investigation to meet the following requirements simultaneously so that the above object is achieved: prevention of fiber slippage within the fibrous sheet for reinforcement, high toughness in the arranged direction of the fibers, and numerous spaces among fibers. As a result, they have elucidated that the problems can be solved only after adopting a specific warp knitting structure.
That is, according to the present invention, the following fibrous sheet for structure reinforcement is provided.
A fibrous sheet for structure reinforcement comprising
a sheet layer of reinforcing continuous filament bundles arranged parallelly spaced out from each other, PA1 auxiliary covering yarns arranged on both sides of said sheet layer in such a manner that each of said covering yarns intersects respective reinforcing filament bundles while meandering along the longitudinal direction of said reinforcing filament bundles on at least one side of said sheet layer, and PA1 auxiliary chain-stitching yarns which interconnects the auxiliary covering yarns on one side of said sheet layer with the auxiliary covering yarns on the other side of said sheet layer through individual spaces among adjacent reinforcing filament bundles in a warp knitting structure.
Furthermore, according to the present invention, the following structure is provided.
A structure formed by covering a structure member to be reinforced with the fibrous sheet for structure reinforcement as mentioned above in the peripheral and/or longitudinal direction through an adhesive.